Thermo Scientific 3403 Manual page 51

Thermo Scientific
If the display does not reflect the correct status, check the corresponding
voltage at TP13 and confirm the presence or absence of the correct
voltage. If an erroneous voltage is being measured by the A/D converter
(outside ±50mV of the anticipated value), 'Error' will be displayed. If this
is the case, check the levels at all other A/D inputs. If all are within range,
0 to 4.5 VDC, the CPU board is most likely to blame.
Conversely, to test the tank switcher assembly, turn on the supply tanks
one at a time and confirm a short on the corresponding pins of the J21
and J22 connectors.
TP4 "VBAT"
When operating correctly, ~14 - 16 VDC is typically present when
loaded with a battery. ~17 - 19 VDC will be present when unloaded.
This will vary with line voltage.
MISC.
J14 Remote Alarm
Pin out is as follows:
Pin 1 – NC
Pin 2 – NO
Pin 3 - Common
A/D Converter Refresher
Fundamental purpose of an A/D converter is to convert an analog voltage
to a digital number.
V
REF
V
IN
GND
Result is basically a ratio of VIN to VREF, normalized to VREF in binary format.
Simplified example:
VOLTAGE
4.5
0
Max
(V
DATA OUT IN
(V
REF
(n-bit)
FFFFFF
(Max.
Count)
Temperature
– GND)
x (Max Count)
– GND)
A/D Output
0
Max
Midi 40 CO2 Incubator
Section 8
Appendices
Temperature
8-19